Efficient x-ray diffractors having a large collection solid angle and high spectral resolving power have surfaces and planes that are cylindrically curved to different radii as in the Johansson geometry, or are doubly curved as in the spherically bent plate or in diffractors with spherical planes and toroidal surface. However, the ideal geometries involving doubly curved diffracting planes and surfaces that are curved differently than the planes cannot always be used for diffractors fabricated from bulk single crystals for several reasons. First, natural crystal are not available with sufficiently large d spacings to diffract long wave length x rays. Second, some natural crystals with desirable d spacings and high diffraction efficiency cannot be formed to the desired configuration because of difficulty in grinding or polishing the surfaces that are not parallel to cleavage planes or because of the tendency to fracture when elastic bending is used or because of the undesirable distortion of the crystal lattice if plastic bending is used. The latter problems are enhanced when using thick pieces of single crystals to form large area diffractors because of the greater stresses produced in bending. On the other hand, layered structures obtained by multiple deposition processes have not yet been made with sufficiently small d spacings to diffract x-rays of short wave length at large Bragg angles and have not been made sufficiently thick to be configurable to the desired geometry.
The purpose of the present invention is to provide a diffractor geometry with a stepped surface that will increase the possible ways for fabricating large area, high efficiency diffractors and will increase the variety and types of diffracting materials that can be used in the fabrication of these diffractors.